Method of making high wet strength paper



Aprii 10, 1951 F. w. BOUGHTON 5 9 METHOD OF MAKING HIGH WET STRENGTHPAPER Filed April 22, 1944 A A- SOD/UM MUM/M475 l6 +Hcl USED in 5mm? EJUBSTANT/ALLY FREE 0F BIVALENT ANIONS w I B- ALUMINUM SULFATE 5 USED INBEATER E 8 G j a 6 k 0 r 2 a 4 s MEL AM/NE-FORMALDEHYDE RES/N (BASED ONBONE-DRY Puuy FRED W. B0 UGH TON INVENTOR wll w A RNEYS Patented Apr.10, 1951 UNITED STATES PATENT OFFICE Eastman Kodak Company, Rochester,N. Y., a corporation of New Jersey Application April 22, 1944, SerialNo. 532,299

Claims.

This invention relates to the preparation of high wet strength paperhaving good flexibility, by first mixing with paper pulp in the beateran ordinary paper sizing and either (1) aluminum chloride, nitrate oracetate or ('2) an alkali metal aluminate plus hydrochloric, acetic ornitric acid; polyvalent inorganic acid ions being always substantiallyabsent from the system employing either (1) or (2) after the pulp hasbeen reduced to final readiness for paper a wet strength-impartingmelamine-formaldehyde resin or melamine-monoureide-formaldehyde resin isincorporated therein.

The obtaining of paper having a high wet strength without detrimentallyaffecting the other properties thereof has been given considerableattention in recent years. In many of the proposed means of maintainingor increasing the wet strength of the paper, the paper has been renderedbrittle or the properties were otherwise altered so that the increasedwet strength has been obained by the sacrifice of some other desirableproperty.

ihe preparation of high wet strength paper has been described in U. S.Patents Nos; 2,291,079 and 2,291,080 of Hoiferbert. In those patents thehigh wet strength of the paper is obtained by the use of aminotriazine-aldehyde condensation products applied as a tub sizing to thepaper (i. e., after the paper is formed and dried) and the final productwhich is obtained, while having an increased wet strength, exhibits amuch lower flexibility than the paper originally treated. As animprovement over the process of the Hofierbert patents it has beensuggested that melamineformaldehyde resin be first dissolved inhydrochloric acid and aged for at least 12 to 24 hours followed by usingthe resulting product as a beater sizing in the regular beater furnishi. e. with alum (aluminum sulfate) as a fluocculent. This procedure hasresulted in a paper showing some improvement in wet strength without anyserious decrease in the flexibility of the paper. I have found, however,that by employing my inventionvastly improved wet strengths may beobtained over the wet strengths obtained by the procedure referred toand-yet the flexibility properties of the paper are not adverselyaffected.

It is an object of my invention to produce a high Wet strength paperhaving good flexibility 2 properties and generally, good stabilitytoward photographic emulsions without adversely affecting the otherproperties of the paper. Other objects of my invention will appearherein.

My invention in its broader aspects comprises a process of making paperof high wet strength particularly adapted to photographic purposes inwhich paper pulp is mixed in the beater with paper' sizing and either(1) an alkali metal aluminate and sufiicient hydrochloric, nitric oracetic acid to precipitate the sizing or (2) sufficient aluminumchloride, nitrate -or acetate, to precipitate the sizing, and before thepaper stock is brought to the paper machine, there is incorporatedtherein a small proportion of a wet strengthimpartingmelamine-formaldehyde resin or melamine monoureide formaldehyde resin,care being taken to carry out the process in the absence of polyvalentinorganic acid radicals.

In the preferred aspect of my invention there is first incorporated inthe pulp in the beater one of the usual beater sizings which isacidified to a pH of 4 to' 5 by the addition of an alkali metalaluminate and hydrochloric, nitric or acetic acid or by the addition ofan aluminum salt of one of those acids. After the pulp has been reducedand before being brought to the paper machine there is added anduniformly distributed therethrough a wet strength-impartingmelamineformaldehyde resin or melamine-monoureideformaldehyde resin.While I have mentioned a pH of 4 to 5 as being the preferred range ofacidity for precipitating the usual beater sizings, it will beunderstood that the principle involved in such acidification is tointroduce the right amount of specified acid to precipitate the sizingwithout having either too much acidity or'too little acidity. Obviouslyno advantage is to be gained by having the furnish more acid thannecessary as this simply results in excess acidity. At the otherextreme, it is not wise to have too little acidity in the furnish forthe reason that incomplete precipitation of the sizing will be effected,with accompanying'loss in economy and quality.

In making paper in accordance with my invention, hydrochloric is thepreferred acid for use with the alkali metal aluminate, being lessexpensive and readily available. Nitric acid maybe employed; however, itis more expensivethan hydrochloric and has oxidizing tendencies whichmay be undesirable with some types of treatment. Acetic acid may beemployed; however, more is required to impart the desired pH than is thecase with hydrochloric acid.

The alkali metal aluminate (with acid) and the aluminum chloride,nitrate or acetate (without acid) perform the function in the furnish ofsupplying the necessary aluminum floc to coagulate the precipitatedsizing, this function of aluminum fioc being well known in the art. Itis desirable with the commercial melamine-formaldehyde resins to firstage them in solution in hydrochloric acid before incorporating in paperpulp in accordance with my invention. Some resins of this type requireconsiderable aging such as standing of their hydrochloric acid solutionfor 24 hours or longer, while in the case of other resins of this typestanding but a short time such as 3 hours is sufiicient; such aging isunderstood by the trade. Aging may be carried out, for example, bydissolving 100 lbs. of commercial melamine-formaldehyde resin in amixture of 50 gallons of water and 48.6 lbs. of commercial hydrochloricacid at a temperature of 130-140 F., adding cold water to make 100gallons and allowing the mass to stand at a temperature less than 100 F.for the desired time, such as approximately 3 to 24 hours.

Melamine-monoureide-formaldehyde resin is described in some detail in U.S. Patent No. 2,312,688 of DAlelio dated March 2, 1943. It isconveniently prepared by first reacting melamine with an equal number ofmoles of urea followed by reaction of the melamine ureide formed, withformaldehyde. For example, 2000 grams of concentrated HCl containing 20moles of hydrogen chloride were added to liters of distilled water and1200 grams of urea (20 moles) were dissolved in this solution. Byreacting 2520 grams of practical grade melamine (20 moles) therewith atan elevated temperature a product consisting essentially of melaminemonoureide may be obtained. The melamine-monoureide was isolated fromthe reaction mixture by crystallization and then dried.

2000 grams (11.83 moles) of the melamine-monoureide thus obtained weredissolved with rapid stirring in a mixture consisting of 16.8 liters ofwater and 5.6 liters (75 moles I-ICHO) 'of commercia140% formalin, themixture being brought r to a temperature of 80 C. before adding theureide. When the ureide had. all dissolved, the solution was rapidlycooled to room temperature. It had a pH of 2.9.

Resins having various molar ratios of formaldehyde to melamine may beemployed as the melamine-formaldehyde resin. For instance, resinsprepared using molar ratios of formaldehyde to melamine of from 1:1 upto 6:1 or even higher can be used. Ordinarily, the resins prepared usinga molar ratio of formaldehyde to melamine between 2:1 and 4:1 are mostsuitable for this operation.

In making paper in accordance with my invention, the pulp is placed inthe beater and, in the beating operation, is sized with one of the usualsizing materials among which may be mentioned rosin, hydrogenated rosinor stearic acid, which has been saponified with caustic soda or thelike. Ordinarily, the size may be prepared from the rosin, hydrogenatedrosin or stearic acid by treating with /3 of its weight of caustic soda.The soap thus formed can be used in any dilution desired. The use oflarger amounts of caustic soda in preparing the soap merely necessitatesthe emiii) ployment of larger proportions of acid in the beater sizingoperation and has other disadvantages. When the sizin is added to thebeater, there is also added sodium aluminate and an acid such ashydrochloric acid in a sufficient amount to precipitate the sizingmaterial and to impart the proper acidity to the paper. Instead ofadding sodium aluminate and acid, the aluminum salt of the monovalentacid may be added such as, for instance, aluminum chloride or aluminumnitrate. If the aluminum salt added is not of sufficient acid strengthto impart the desired acidity to the paper when used in small quantity,additional acid (herein specified) should also be incorporated in thebeater mass to bring the mass to the acidity desired. It is desirable,particularly if the paper being prepared is to be used for photographicpurposes, to reduce the' acidity of the pulp to a pH of approximately 4to 5.

After the beating operation i completed and the pulp has been reduced soas to be ready for forming paper, such as after the pulp has been putthrough the Jordan, a small amount of a wet strength-imparting resinabove specified is added thereto in proper proportion. The paper stockis then ready for deposit on the wire of the paper machine and paper isprepared therefrom.

I have found that the papers resulting from treatment with the wetstrength-imparting resins herein specified, when substantially free ofpolyvalent inorganic acid ions, possess wet strengths considerablyhigher than paper in which those ions are present. I have also foundthat to obtain a specified wet strength a much less quan tity of theresin is necessary when sodium aluminate and hydrochloric, nitric oracetic acid are employed or when their aluminum salt is employed, thanin those cases in which polyvalent inorganic acid ions are employed inany of the operations in sizing the pulp in the beater. For instance, ahigh wet strength paper prepared in accordance with my process, usingsodium aluminate and hydrochloric acid together with the sizing materialin the beater, and adding 3% of wet strength-impartingmelamine-formaldehyde resin before placing on the wire of the papermachine, the operation carried out in such a manner as to produce apaper weighing 21 lbs. per 1000 square feet, gave a product having a wetstrength of 17% pounds per square inch whereas a similar pulp using thesame sizing material but employing only aluminum sulfate (the conventional material) to precipitate the size in the beater and thenadding 3% of the resin before placing on the wire of the paper machinegave a paper, when of the same base weight, having a wet strength ofonly 8 pounds per square inch. In another instance in which only l /2%of the resin was employed, the paper in which the sodium aluminate andmonovalent acid was used (polyvalent inorganic acid ions being absent)gave a wet strength of 11 whereas, when aluminum sulfate only wasemployed for acidifying the beater size, the other conditions being thesame, a wet strength of only 5% was obtained.

The drawing is for the purpose of illustrating the distinction betweenthe wet strengths of paper sheets prepared inthe absence of polyvalentinorganic acid ions and those in which aluminum sulfate is employed inthe beater. It may be seen from this graph that to obtain a wet strengthof is used. The data employed for this graph was obtained by processingbeater stock and handling over the paper machine in a regular mannerexcept that in one case the stock was prepared using, in the beater toacidify the pulp, sodium aluminate and hydrochloric acid and in theother aluminum sulfate. The beater compositions for the two cases wereas follows:

Sodium Aluminate Treatment Aluminum Sulfate Treatment 1100 gals. water.

9.6 lbs. sodium stearate. 11.1 lbs. gelatine.

45 lbs. cooked corn starch. 16.7 lbs. aluminum sulfate.

The paper sheets prepared in each case had a base weight of 20 lbs. per1000 square feet.

The resin employed was a melamine-formalde hyde resin marketed as PaperMakers Resin No. 607 which had been aged by allowing the solution of theresin in aqueous hydrochloric acid normal) to stand for approximately 3hours. The acid-resin solution was added to the stock after theJordaning operation in every case.

It may be seen from the attached graph that even a very small proportionof resin will increase wet strength in accordance with my invention. Inmost cases it is preferred to use at least 4% of resin. Ordinarily, notmore than 5% is necessary to give the desired wet strength although afurther amount such as up to or even more may be incorporated ifdesired. Normally A;-l% of resin based on the bone dry weight of thepulp is the preferred operating range. Other materials than those listedsuch as starch, glues, dyes and the like may be employed as an additionto the paper pulp provided they do not introduce any substantial amountof sulfate radical or some other polybasic inorganic acid radical to themass. The sole criterion as to the amount of polyvalent acid radicalwhich can be tolerated is that which does not materially affect the wetstrength of the paper which is obtained. It has been my experience thatsome polybasic inorganic acids are less liable to,lower the wet strengthof the paper obtained than are other acids of this nature. It is .to beunderstood that the term substantially free of polyvalent inorganic acidions when applied to paper is to be understood to mean that polyvalentacid ions are not present in an amount to exert any more substantialeffect upon the wet strength than would be obtained by their completeomission.

Roughly the same wet strength is obtained when using the sameproportions of melaminemonoureide-formaldehyde resin in the system underthe same conditions, as is described above and illustrated in the graphin the case of melamine-formaldehyde resin.

The wet strengths referred to in this application were determined bymeans of an Ashcroft tester, the values given being in pounds per squareinch. In determining these values, the paper was first soaked in waterfor two hours at 70 F. before being tested.

The invention may be carried out usingany customary paper pulp. Althoughhigh a-CSlllllose sulfite pulp was employed in most of the operationsdescribed herein, other types of wood pulp or rag stock or recoveredwaste fiber may be employed as the starting materialfor making paper inaccordance with my invention. The

' ing operation.

sizing material isusually used in an amount on the order of l of thebone dry weight of the pulp although this proportion may be varied asdesired. The acid employed to precipitate the sizing is preferably anystrong monobasic acid particularly if the acid has no detrimental effectupon the properties of the paper.

As related above, in some cases it may be desired to employ the aluminumsalt of a monobasic acid to acidify the pulp in the beater. Forinstance, aluminum-chloride is eminently suitable for this purpose andeliminates the difficulty of handling large volumes of acid in the papermak- Instead of aluminum chloride, aluminum nitrate or acetate may beemployed. Sometimes it may be desirable to supplement the salt with anaddition of hydrochloric acid to supply the desired degree of acidity.

The following examples illustrate my invention:

Example 1 A refined sulfite wood pulp was placed in a hollander orbeater to which was added approximately 1% of hydrogenated rosin sizeand. approximately 1% of sodium aluminate, the percentages being basedupon the bone dry Weight of the pulp. The hydrogenated rosin sizeemployed was prepared by saponifying hydrogenated rosin withapproximately its weight of caustic soda. Approximately 5% (based on thebone dry weight of the pulp) of 35% hydrochloric acid was added to thebeater, thus precipitating the sizing materials of the pulp. After thebeating treatment had been completed and after the pulp had been putthrough a Jordaning operation but before the paper stock was brought tothe paper machine, there was added thereto 1% (based on the weight ofthe bone dry pulp) of an acid-aged wet strength impartingmelamine-formaldehyde resin (No. 607) in solution in hydrochloric acid.The paper stock was then applied to the wire of the paper machine andpaper was prepared therefrom and passed through the remainder of themachine in the conventional manner. The paper having a base weight of 20lbs. per 1000 sq. ft. exhibited a wet strength of 12 lbs. per squareinch.

Example 2 600 pounds of sulfite pulp in suspension in 1100 gallons ofwater were mixed in the beater with 10 pounds of sodium stearate, 45pounds of corn starch and 15 pounds, of aluminum chloride, the materialsbeing added to the water in the beater in the order given. After thebeating treatment had been completed and the pulp had been put through aJordaning operation, acid-aged melamine-formaldehyde resin (No. 607') insolution in hydrochloric acid was added to the stock in an amount of thebone dry pulp. The resultant stock was then processed over a papermachine in the conventional manner. The wet strength of this paper wasdetermined by soaking for two hours in water at 70 F. and testing in anAshcrofttester. The wet strength of the paper was found to be 25 poundsper square inch. The paper processed in an identical manner but usingaluminum sulfate to impart acidity in the beater gave a wet strength ofapproximately 10 pounds per square inch. The papers compared both had abase weight of. 52 pounds per 1000 square feet.

Example 3 600 pounds of sulfite pulpin suspension in 1100 gallons ofwater were mixed in the beater with the following added in the ordergiven:

5.6 lbs. of sodium aluminate 9.6 lbs. of sodium stearate 3.0 lbs. ofgelatin 45.0 lbs. of cooked corn starch gallons of hydrochloric acid(24%) After the beating had been completed and the pulp had been Jordanned, melamine-monoureideformaldehyde in solution in hydrochloricacid was added to the stock in an amount of the weight of bone dry pulp.A paper sheet was formed therefrom (base weight '20 pounds per 1000square feet) which exhibited a wet strength of 28 pounds per squareinch.

There are, of course, types of paper which do not require sizing and, infact, in which sizing is not even desired such, for instance, as papertowelling and the like which need to be highly water absorptive but atthe same time must maintain high wet strength. My invention is as usefulfor such unsized papers as it is for photographic paper, for instance,where a sizing is customary. In producing most paper stock, it isdesirable to have the furnish on the acid side to prevent foaming etcetera, and it might be thought that one could produce such unsizedpapers by merely omitting the sizing and by employing the customaryaluminum sulfate to obtain the desired acidity. However, I have foundthat even in the absence of sizing, one does not obtain as high wetstrength when employing aluminum sulfate as the acidifier as one obtainsby omitting substantially all polyvalent inorganic acid radicals fromthe furnish and using either hydrochloric acid, nitric acid, or aceticacid as the acidifier in conjunction with the resins which I have aboveoutlined as being wet strength-imparting resins. Thus a water absorptivehigh wet strength unsized paper can be produced by a furnish make-upconsisting of water, suitable paper pulp and a melamine-formaldehyderesin or -melamine-monoureide-formaldehyde resin, with a strongmonobasic acid such as hydrochloric acid, nitric acid, or acetic acid asthe acidifier, all polyvalent inorganic acid ions being substantiallyabsent from the furnish. An example of the preparation of such a furnishis as follows:

Example 4 600 pounds of sulfite pulp in suspension in 1100 gallons ofwater were mixed in the beater with 1 /2 gallons of aqueous hydrochloricacid (24% concentration) reducing the pH of the mass to approximately4.5. After the beating treatment had been completed and the pulp hadbeen put through a Jordanning operation 3% (based on the bone dry weightof the pulp) of acid-aged melamine-formaldehyde resin (No. 607) insolution in hydrochloric acid was added to the stock. The resultantstock was then processed on the paper machine in the conventional mannerto form a paper sheet highly absorbent to water. The paper sheet had aweight of 14 pounds per 1000 square feet and when tested on the Ashcrofttester exhibited a wet strength of 18 pounds per square inch. Normalpaper making pH is ordinarily within the range of 4-6.5 and in order toobtain this pH an acidifying agent is added to the beater. In myinvention this acidifying agent is either aluminum chloride, aluminumnitrate, or aluminum acetate. The pH obtained by this addition isconducive both to precipitation of the beater sizing and condensation ofthe resin added to impart higher wet strength in paper makingoperations. This is true with respect to all of the resins which I haveadvocated employing herein. The strength of the strong monobasic acid inthe furnish is sufiicient to give to the furnish a pH of 4 to 6.5.

It is to be understood that the strong monobasic acid desired althoughusually supplied by direct addition to the pulp mass where acidificationis desired, may also be supplied by addition of an acid salt of a strongmonobasic acid. This is illustrated by the use of aluminum chloridewhich supplied both hydrochloric acid and aluminum 1100. Other salts ofstrong monobasic acids which impart a lower pH to the mass such asammonium chloride, et cetera may be employed for this purpose ifdesired.

If desired the operator may employ alum for the acidification of thepulp followed by treatment with barium, calcium or strontium chloride toprecipitate the sulfate ions and thus assure the absence of sulfate ionsin the final product. It is to be understood that such a procedure alsocomes within the scope of my invention as defined by the appendedclaims.

I claim:

1. A method of making high wet strength paper which comprises beatersizing paper pulp with an acid precipitable sizing material, addingthereto in sufficient amount to precipitate the sizing and impart a pHof 4-6.5 an aluminum material selected from the group consisting of analkali metal aluminate plus hydrochloric acid, an alkali metal aluminateplus acetic acid, an alkali metal aluminate plus nitric acid, aluminumchloride, aluminum nitrate and aluminum acetate, incorporating in thepulp A -5%, based on the bone dry weight of the pulp, of a wetstrength-imparting resin selected from the group consisting of themelamine-formaldehyde resins and the melamine-monoureide-formaldehyderesins, and forming paper therefrom.

2. A method of making high wet strength paper which comprises beatersizing paper pulp with an acid precipitable sizing material, addingsodium aluminate and hydrochloric acid thereto in sufficient amount toprecipitate the sizing and impart a pH of 46.5, incorporating in thepulp /4--5%, based on the bone-dry weight of the pulp, of a wetstrength-imparting resin selected from the group consisting of themelamine-formaldehyde resins and the melamine-monoureide-formaldehyderesins and forming paper therefrom.

3. A method of making high wet strength paper which comprises beatersizing paper pulp with an acid precipitable sizing material, addingthereto aluminum chloride, in suflicient amount to precipitate thesizing and impart a pH of 4 to 6.5, incorporating in the pulp 4-23%,based on the bone-dry weight of the pulp, of a wet strength impartingresin selected from the group consisting of the melamine-formaldehyderesins and the melamine-monoureide-fcrmaldehyde resins and forming papertherefrom.

4. A method of making high wet strength paper which comprises beatersizing paper pulp with sodium stearate size, adding aluminum chloridethereto in sufficient amount to precipitate the sizing and impart a pHof 4-6.5, followed by incorporating inthe pulp 1% (based on the bone-dryweight of the pulp) of a melamineformaldehyde wet strength-impartingresin and forming paper from the pulp.

5. A method of making high wet strength paper which comprises beatersizing paper pulp with an acid precipitable sizing material, addingthereto aluminum chloride in sufficient amount to precipitate the sizingand impart a pH of 4 to 6.5, incorporating in the pulp 44% based on thebone-dry weight of the pulp of melamine-formaldehyde wetstrength-imparting resin and forming paper therefrom.

FRED W. BOUGHTON.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 452,143 Menzies May 12, 18911,714,052 Spencer May 21, 1929 2,116,768 Rowland May 10, 1938 2,291,078Hofferbert July 28, 1942 2,291,080 Hofi'erbert July 28, 1942 2,312,688DAlelio Mar. 2, 1943 2,345,543

Wohnsiedler Mar. 28, 1944 OTHER, REFERENCES Paper Trade Journal, Dec. 2,1943, pages 27-32. Paper Trade Journal, May 13, 1943, pages 39-42. PaperTrade Journal, Mar. 6, 1941, pages 35 and 36.I

Resins for Paper Manufacture published by American Cyanamid and ChemicalCorp., 30 Rockefeller Plaza, New York, July 20, 1942, 3 pages.

Technical Association Papers of the Pulp and Paper Industry, Series 19(1936) page 471.

1. A METHOD OF MAKING HIGH WET STRENGTH PAPER WHICH COMPRISES BEATERSIZING PAPER PULP WITH AN ACID PRECIPITABLE SIZING MATERIAL, ADDINGTHERETO IN SUFFICIENT AMOUNT TO PRECIPITATE THE SIZING AND IMPART A PHOF 4-6.5 AN ALUMINUM MATERIAL SELECTED FROM THE GROUP CONSISTING OF ANALKALI METAL ALUMINATE PLUS HYDROCHLORIC ACID, AN ALKALI METAL ALUMINATEPLUS ACETIC ACID, AN ALKALI METAL ALUMINATE PLUS NITRIC ACID, ALUMINUMCHLORIDE, ALUMINUM NITRATE AND ALUMINUM ACETATE, INCORPORATING IN THEPULP 1/4-5%, BASED ON THE BONEDRY WEIGHT OF THE PULP, OF A WETSTRENGTH-IM PARTING RESIN SELECTED FROM THE GROUP CONSISTING OF THEMELAMINE-FORMALDEHYDE RESINS AND THE